Methods and systems for estimating a flow of gases in a scavenge exhaust gas recirculation system of a split exhaust engine system

ABSTRACT

Methods and systems are provided for adjusting operation of a split exhaust engine system based on a total flow of gases through a scavenge exhaust gas recirculation system of the split exhaust engine system. In one example, a method may include adjusting engine operation in response to a flow of gases to an intake passage, upstream of a compressor, from a scavenge manifold coupled to scavenge exhaust valves, the flow of gases determined based on a valve opening overlap between the scavenge exhaust valves and intake valves of an engine, the scavenge exhaust valves opened at a different time than blowdown exhaust valves coupled to a blowdown manifold coupled to a turbine.

FIELD

The present description relates generally to methods and systems for anengine having a split exhaust system.

BACKGROUND/SUMMARY

Engines may use boosting devices, such as turbochargers, to increaseengine power density. However, engine knock may occur due to increasedcombustion temperatures. Knock is especially problematic under boostedconditions due to high charge temperatures. The inventors herein haverecognized that a split exhaust system, where a first exhaust manifoldroutes exhaust to a turbine of the turbocharger in an exhaust of theengine and a second exhaust manifold routes exhaust gas recirculation(EGR) to an intake of the engine, upstream of a compressor of theturbocharger, may decrease engine knock and increase engine efficiency.In such an engine system, each cylinder may include two intake valvesand two exhaust valves, where a first set of cylinder exhaust valves(e.g., blowdown exhaust valves) are exclusively coupled to the firstexhaust manifold via a first set of exhaust ports, and a second set ofcylinder exhaust valves (e.g., scavenge exhaust valves) are exclusivelycoupled to the second exhaust manifold via a second set of exhaustports. The first set of cylinder exhaust valves may be operated at adifferent timing than the second set of cylinder exhaust valves, therebyisolating a blowdown portion and a scavenging portion of exhaust gases.The timing of the second set of cylinder exhaust valves may also becoordinated with a timing of the cylinder intake valves to create apositive valve overlap period where fresh intake air (or a mixture offresh intake air and EGR), referred to as blowthrough, may flow throughthe cylinders and back to the intake, upstream of the compressor, via anEGR passage coupled to the second exhaust manifold. Blowthrough air mayremove residual exhaust gases from within the cylinders (referred to asscavenging). The inventors herein have recognized that by flowing afirst portion of the exhaust gas (e.g., higher pressure exhaust) throughthe turbine and a higher pressure exhaust passage and flowing a secondportion of the exhaust gas (e.g., lower pressure exhaust) andblowthrough air to the compressor inlet, combustion temperatures can bereduced while increasing a work efficiency of the turbine and increasingengine torque.

However, the inventors herein have recognized potential issues with suchsystems. As one example, in the engine system described above, a flowmeasurement and/or composition of the recirculated gases flowing throughthe EGR passage may be difficult to obtain. However, these measurementsmay be necessary for accurate scavenge exhaust system control. Forexample, previous methods of measuring flow through the EGR valve in theEGR passage utilize a delta pressure measurement system and an orificeflow equation. However, this measurement requires a significantrestriction resulting in a high delta pressure across the orifice, suchas obtained by using a rocket nozzle or venturi design, in order toensure a high signal to noise ratio. This significant pressure dropneeded for flow measurement may limit engine performance at high loadconditions due to limiting flow through the EGR and/or intake system.

In one example, the issues described above may be addressed by a methodcomprising: adjusting engine operation in response to a flow of gases toan intake passage, upstream of a compressor, from a scavenge manifoldcoupled to scavenge exhaust valves, the flow of gases determined basedon a valve opening overlap between the scavenge exhaust valves andintake valves of an engine, the scavenge exhaust valves opened at adifferent time than blowdown exhaust valves coupled to a blowdownmanifold coupled to a turbine. In one example, the flow of gases may bea total flow gases through a scavenge EGR system, from the scavengemanifold to the intake passage. Additionally, the valve opening overlapmay be a valve opening overlap area, determined based on valve lifts ofeach of the scavenge exhaust valves and the intake valves. In someexamples, the total flow of gases may be further determined based on anintake manifold pressure and scavenge manifold pressure. By adjustingengine operation in response to the determined total flow of gases basedon the above-described valve overlap area and pressure measurements,engine efficiency may be increased without limiting engine performanceat high loads.

It should be understood that the summary above is provided to introducein simplified form a selection of concepts that are further described inthe detailed description. It is not meant to identify key or essentialfeatures of the claimed subject matter, the scope of which is defineduniquely by the claims that follow the detailed description.Furthermore, the claimed subject matter is not limited toimplementations that solve any disadvantages noted above or in any partof this disclosure.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a schematic depiction of a turbocharged engine system witha split exhaust system.

FIG. 2 shows an embodiment of a cylinder of the engine system of FIG. 1.

FIG. 3 shows example cylinder intake valve and exhaust valve timings forone engine cylinder of a split exhaust engine system.

FIGS. 4A-4D schematically illustrate sources of different recirculatedgases throughout an open duration of the scavenge exhaust valve withrespect to example engine positions.

FIG. 5 shows an example map of a relationship between scavenge manifoldmass fractions of scavenge manifold gas portions and an amount ofscavenge valve and intake valve overlap.

FIGS. 6A-6B show example valve timing diagrams for different amounts ofscavenge valve and intake valve overlap.

FIG. 7 shows a flow chart of an example method for determining totalflow through a scavenge exhaust gas recirculation passage and relativeconcentrations of burnt gases, fuel, and air within the total flow.

FIG. 8 shows adjustments to engine operating parameters based on changesin the determined total flows of burnt gases, fresh air, and unburnedhydrocarbons through the scavenge exhaust gas recirculation passage.

DETAILED DESCRIPTION

The following description relates to systems and methods for operating asplit exhaust engine with blowthrough and exhaust gas recirculation(EGR) to an intake via a scavenge manifold and adjusting engineoperation based on a flow amount and concentration of gases recirculatedto an intake passage via a scavenge EGR system. An example of a splitexhaust engine including a scavenge EGR system is shown in FIG. 1. Inone embodiment, the engine may be installed in a hybrid vehicle system,such as the vehicle system of FIG. 2. As shown in the cylinder valvetiming diagram of FIG. 3, a valve overlap period occurs between thescavenge exhaust valve (e.g., second exhaust valve) and the intakevalves, where these valves are open at the same time. During this valveoverlap period, which may vary in length based on valve timings,different gas portions from different sources may enter the scavengeexhaust manifold (and thus be recirculated to the intake passage), asshown by FIGS. 4A-4D. Each of these different gas portions may containdifferent concentrations of burnt gases, fresh air, and unburnedhydrocarbons. The relative mass fractions of the different recirculatedgas portions (including intake gases, pushback gases, and combustionproducts) may vary based on the amount of valve overlap between theintake valves and scavenge valves, as illustrated by the map shown inFIG. 5. Example valve timing diagrams for the extreme overlap amounts ofFIG. 5 are shown in FIGS. 6A-6B. The total bulk flow recirculated to theintake passage from the scavenge manifold, via the scavenge EGR passage,may be determined based on a valve overlap area between the scavengevalve and intake valves and pressures in the intake manifold andscavenge manifold, as shown by the method of FIG. 7. The method of FIG.7 further includes using a relationship, such as the map presented inFIG. 5, along with the determined total flow to determine individualtotal flows for each of burnt gases, unburned hydrocarbons, and freshair recirculated via the scavenge EGR passage. In this way, theconcentrations of the individual constituents (e.g., burnt gas, air, andfuel) within the total bulk scavenge EGR flow may be learned and used toadjust engine operation. As a result, engine efficiency may beincreased.

Turning now to the figures, FIG. 1 shows a schematic diagram of anengine system including a multi-cylinder internal combustion engine 10,which may be included in a propulsion system of a vehicle 100. Engine 10includes a plurality of combustion chambers (e.g., cylinders), which maybe capped on the top by a cylinder head. In the example shown in FIG. 1,engine 10 includes cylinders 13, 14, 15, and 18, arranged in an inline-4configuration. Cylinders 14 and 15 are referred to herein as the inner(or inside) cylinders, and cylinders 13 and 18 are referred to herein asthe outer (or outside) cylinders. However, it should be understood thatalthough FIG. 1 shows four cylinders, engine 10 may include any numberof cylinders in any configuration, e.g., V-6, I-6, V-12, opposed 4, etc.Further, the cylinders shown in FIG. 1 may have a cylinderconfiguration, such as the cylinder configuration shown in FIG. 2, aswill be further described below.

Each of cylinders 13, 14, 15, and 18 include two intake valves,including a first intake valve 2 and a second intake valve 4, and twoexhaust valves, including a first exhaust valve (referred to herein as ablowdown exhaust valve, or blowdown valve) 8 and a second exhaust valve(referred to herein as a scavenge exhaust valve, or scavenge valve) 6.The intake valves and exhaust valves may be referred to herein ascylinder intake valves and cylinder exhaust valves, respectively. Asexplained below with reference to FIG. 2, a timing (e.g., openingtiming, closing timing, opening duration, etc.) of each of the intakevalves may be controlled via various camshaft timing systems. In oneexample, both of the first intake valves 2 and the second intake valves4 may be controlled to a same valve timing, such that they open andclose at the same time in the engine cycle. In an alternative example,the first intake valves 2 and the second intake valves 4 may becontrolled at a different valve timing. Further, the first exhaustvalves 8 may be controlled at a different valve timing than the secondexhaust valves 6, such that the first exhaust valve and the secondexhaust valve of a same cylinder open and close at different times thanone another and the intake valves, as further discussed below.

Each cylinder receives intake air (or a mixture of intake air andrecirculated exhaust gas, as will be elaborated below) from an intakemanifold 44 via an air intake passage 28. Intake manifold 44 is coupledto the cylinders via intake ports (e.g., runners). For example, intakemanifold 44 is shown coupled to each first intake valve 2 of eachcylinder via a first intake port 20. Further, intake manifold 44 iscoupled to each second intake valve 4 of each cylinder via a secondintake port 22. In this way, each cylinder intake port can selectivelycommunicate with the cylinder it is coupled to via a corresponding oneof the first intake valves 2 or second intake valves 4. Each intake portmay supply air, recirculated exhaust gas, and/or fuel to the cylinder itis coupled to for combustion.

One or more of the intake ports may include a charge motion controldevice, such as a charge motion control valve (CMCV). As shown in FIG.1, each first intake port 20 of each cylinder includes a CMCV 24. CMCVs24 may also be referred to as swirl control valves or tumble controlvalves. CMCVs 24 may restrict airflow entering the cylinders via firstintake valves 2. In the example of FIG. 1, each CMCV 24 may include avalve plate; however, other configurations of the valve are possible.Note that for the purposes of this disclosure, the CMCV 24 is in the“closed” (e.g., fully closed) position when it is fully activated andthe valve plate is fully tilted into the respective first intake port20, thereby resulting in maximum air charge flow obstruction.Alternatively, the CMCV 24 is in the “open” (e.g., fully open) positionwhen deactivated and the valve plate is fully rotated to liesubstantially parallel with airflow, thereby considerably minimizing oreliminating airflow charge obstruction. The CMCVs may be principallymaintained in their “open” position and may only be activated “closed”when swirl conditions are desired. As shown in FIG. 1, only one intakeport of each cylinder includes CMCV 24. However, in other examples, bothintake ports of each cylinder may include a CMCV 24. A controller 12 mayactuate CMCVs 24 (e.g., via a valve actuator that may be coupled to arotating shaft directly coupled to each CMCV 24) to move the CMCVs intothe open or closed positions, or a plurality of positions between theopen and closed positions, in response to engine operating conditions(such as engine speed/load and/or when blowthrough via the secondexhaust valves 6 is active. As referred to herein, blowthrough air orblowthrough combustion cooling (BTCC) may refer to intake air that flowsfrom the one or more intake valves of each cylinder to second exhaustvalves 6 during a valve opening overlap period between the intake valvesand second exhaust valves 6 (e.g., a period when both the intake valvesand second exhaust valves 6 are open at the same time), withoutcombusting the blowthrough air.

A high pressure, dual stage fuel system (such as the fuel system shownin FIG. 2) may be used to generate fuel pressures at a fuel injector 66coupled to each cylinder. As such, fuel may be directly injected intothe cylinders via fuel injectors 66. A distributorless ignition system88 provides an ignition spark to cylinders 13, 14, 15, and 18 via sparkplugs 92 in response to a signal from controller 12 to initiatecombustion.

Cylinders 13, 14, 15, and 18 are each coupled to two exhaust ports forchanneling blowdown and scavenging portions of the combustion gasesseparately via a split exhaust system. Specifically, as shown in FIG. 1,cylinders 14 and 15 exhaust a first, blowdown portion of the combustiongases to a first manifold portion 81 of a first exhaust manifold (alsoreferred to herein as a blowdown manifold) 84 via first exhaust ports(e.g., runners) 86 and a second, scavenging portion of the combustiongases to a second exhaust manifold (also referred to herein as ascavenge manifold) 80 via second exhaust ports (e.g., runners) 82.Cylinders 13 and 18 exhaust the first blowdown portion of the combustiongases to a second manifold portion 85 of first exhaust manifold 84 viafirst exhaust ports 86 and the second, scavenging portion to secondexhaust manifold 80 via second exhaust ports 82. That is, first exhaustports 86 of cylinders 13 and 18 extend from cylinders 13 and 18 to thesecond manifold portion 85 of first exhaust manifold 84, whereas firstexhaust ports 86 of cylinders 14 and 15 extend from cylinders 14 and 15to the first manifold portion 81 of first exhaust manifold 84. Secondexhaust ports 82 extend from cylinders 13, 14, 15, and 18 to secondexhaust manifold 80.

Each exhaust port can selectively communicate with the cylinder it iscoupled to via the corresponding exhaust valve. For example, secondexhaust ports 82 communicate with their respective cylinders via secondexhaust valves 6, and first exhaust ports 86 communicate with theirrespective cylinders via first exhaust valves 8. Second exhaust ports 82are isolated from first exhaust ports 86 when at least one exhaust valveof each cylinder is in a closed position. Exhaust gases may not flowdirectly between second exhaust ports 82 and first exhaust ports 86. Theexhaust system described above may be referred to herein as a splitexhaust system, where a first portion of exhaust gases from eachcylinder are output to first exhaust manifold 84 and a second portion ofexhaust gases from each cylinder are output to second exhaust manifold80, and where the first and second exhaust manifolds do not directlycommunicate with one another (e.g., no passage directly couples the twoexhaust manifolds to one another, and thus the first and second portionsof exhaust gases do not mix with one another within the first and secondexhaust manifolds).

Engine 10 includes a turbocharger including a dual-stage exhaust turbine164 and an intake compressor 162 coupled on a common shaft (not shown).Dual-stage turbine 164 includes a first turbine 163 and a second turbine165. First turbine 163 is directly coupled to first manifold portion 81of first exhaust manifold 84 and receives exhaust gases only fromcylinders 14 and 15 via first exhaust valves 8 of cylinders 14 and 15.Second turbine 165 is directly coupled to second manifold portion 85 offirst exhaust manifold 84 and receives exhaust gases only from cylinders13 and 18 via first exhaust valves 8 of cylinders 13 and 18. Rotation ofthe first and second turbines drives rotation of compressor 162,disposed within the intake passage 28. As such, the intake air becomesboosted (e.g., pressurized) at the compressor 162 and travels downstreamto intake manifold 44.

Exhaust gases exit both first turbine 163 and second turbine 165 into acommon exhaust passage 74. A wastegate may be coupled across thedual-stage turbine 164. Specifically, wastegate valve 76 may be includedin a bypass 78 coupled between each of the first manifold portion 81 andsecond manifold portion 85, upstream of an inlet to dual-stage turbine164, and exhaust passage 74, downstream of an outlet of dual-stageturbine 164. In this way, a position of wastegate valve 76 controls anamount of boost provided by the turbocharger. For example, as an openingof wastegate valve 76 increases, an amount of exhaust gas flowingthrough bypass 78 and not through dual-stage turbine 164 may increase,thereby decreasing an amount of power available for driving dual-stageturbine 164 and compressor 162. As another example, as the opening ofwastegate valve 76 decreases, the amount of exhaust gas flowing throughbypass 78 decreases, thereby increasing the amount of power availablefor driving dual-stage turbine 164 and compressor 162. In alternativeexamples, engine 10 may include a single stage turbine where all exhaustgases from the first exhaust manifold 84 are directed to an inlet of asame turbine.

After exiting dual-stage turbine 164, exhaust gases flow downstream inexhaust passage 74 to a first emission control device 70 and a secondemission control device 72, second emission control device 72 arrangeddownstream in exhaust passage 74 from first emission control device 70.Emission control devices 70 and 72 may include one or more catalystbricks, in one example. In some examples, emission control devices 70and 72 may be three-way catalysts. In other examples, emission controldevices 70 and 72 may include one or a plurality of a diesel oxidationcatalyst (DOC) and a selective catalytic reduction catalyst (SCR). Inyet another example, second emission control device 72 may include agasoline particulate filter (GPF). In one example, first emissioncontrol device 70 may include a catalyst and second emission controldevice 72 may include a GPF. After passing through emission controldevices 70 and 72, exhaust gases may be directed out to a tailpipe.

Exhaust passage 74 further includes a plurality of exhaust sensors inelectronic communication with controller 12, which is included in acontrol system 17, as will be further described below. As shown in FIG.1, exhaust passage 74 includes a first oxygen sensor 90 positionedbetween first emission control device 70 and second emission controldevice 72. First oxygen sensor 90 may be configured to measure an oxygencontent of exhaust gas entering second emission control device 72.Exhaust passage 74 may include one or more additional oxygen sensorspositioned along exhaust passage 74, such as a second oxygen sensor 91positioned between dual-stage turbine 164 and first emission controldevice 70 and/or a third oxygen sensor 93 positioned downstream ofsecond emission control device 72. As such, second oxygen sensor 91 maybe configured to measure the oxygen content of the exhaust gas enteringfirst emission control device 70, and third oxygen sensor 93 may beconfigured to measure the oxygen content of exhaust gas exiting secondemission control device 72. In one example, one or more of oxygen sensor90, oxygen sensor 91, and oxygen sensor 93 may be universal exhaust gasoxygen (UEGO) sensors. Alternatively, a two-state exhaust gas oxygensensor may be substituted for one or more of oxygen sensors 90, 91, and93. Exhaust passage 74 may include various other sensors, such as one ormore temperature and/or pressure sensors. For example, as shown in FIG.1, a sensor 96 is positioned within exhaust passage 74 between firstemission control device 70 and second emission control device 72. Sensor96 may be a pressure and/or temperature sensor. As such, sensor 96 maybe configured to measure the pressure and/or temperature of exhaust gasentering second emission control device 72.

Both sensor 96 and oxygen sensor 90 are arranged within exhaust passage74 at a point where a flow passage 98 couples to exhaust passage 74.Flow passage 98 may be referred to herein as a scavenge manifold bypasspassage (SMBP) 98. Scavenge manifold bypass passage 98 is directlycoupled to and between second exhaust (e.g., scavenge) manifold 80 andexhaust passage 74. A valve 97 (referred to herein as a scavengemanifold bypass valve, SMBV) is disposed within scavenge manifold bypasspassage 98 and is actuatable by controller 12 to adjust an amount ofexhaust flow from second exhaust manifold 80 to exhaust passage 74, at alocation between first emission control device 70 and second emissioncontrol device 72.

Second exhaust manifold 80 is directly coupled to a first exhaust gasrecirculation (EGR) passage 50. First EGR passage 50 is a coupleddirectly between second exhaust manifold 80 and intake passage 28,upstream of compressor 162 (and thus, first EGR passage 50 may bereferred to as a low-pressure EGR passage). As such, exhaust gases (orblowthrough air, as explained further below) is directed from secondexhaust manifold 80 to air intake passage 28, upstream of compressor162, via first EGR passage 50. As shown in FIG. 1, first EGR passage 50may include an EGR cooler 52 configured to cool exhaust gases flowingfrom second exhaust manifold 80 to intake passage 28 and may furtherinclude a first EGR valve 54 (which may be referred to herein as a BTCCvalve) disposed therein. Controller 12 is configured to actuate andadjust a position of BTCC valve 54 in order to control a flow rateand/or amount through first EGR passage 50. When the BTCC valve 54 is ina closed (e.g., fully closed) position, no exhaust gases or intake airmay flow from second exhaust manifold 80 to intake passage 28, upstreamof compressor 162. Further, when the BTCC valve 54 is in an openposition (e.g., from partially open to fully open), exhaust gases and/orblowthrough air may flow from second exhaust manifold 80 to intakepassage 28, upstream of compressor 162. Controller 12 may additionallyadjust the BTCC valve 54 into a plurality of positions between fullyopen and fully closed. In other examples, controller 12 may only adjustBTCC valve 54 to be either fully open or fully closed. Further, apressure sensor 53 may be arranged in EGR passage 50 upstream of BTCCvalve 54.

A first ejector 56 is positioned at an outlet of EGR passage 50, withinintake passage 28. First ejector 56 may include a constriction orventuri that provides a pressure increase at the inlet of compressor162. As a result, EGR from EGR passage 50 may be mixed with fresh airflowing through intake passage 28 to compressor 162. Thus, EGR from EGRpassage 50 may act as the motive flow on first ejector 56. In analternative example, there may not be an ejector positioned at theoutlet of EGR passage 50. Instead, an outlet of compressor 162 may beshaped as an ejector that lowers the gas pressure to assist in EGR flow(and thus, in this example, air is the motive flow and EGR is thesecondary flow). In yet another example, EGR from EGR passage 50 may beintroduced at a trailing edge of a blade of compressor 162, therebyallowing blowthrough air to be delivered to intake passage 28 via EGRpassage 50. An intake pressure sensor 51 may be arranged immediatelyupstream of the venturi of first ejector 56.

A second EGR passage 58 is coupled between first EGR passage 50 andintake passage 28. Specifically, as shown in FIG. 1, second EGR passage58 is coupled to first EGR passage 50 between BTCC valve 54 and EGRcooler 52. In other examples, when second EGR passage 58 is included inthe engine system, the system may not include EGR cooler 52.Additionally, second EGR passage 58 is directly coupled to intakepassage 28, downstream of compressor 162. Further, as shown in FIG. 1,second EGR passage 58 is coupled to intake passage 28 upstream of acharge air cooler (CAC) 40. CAC 40 is configured to cool intake air(which may be a mixture of fresh intake air from outside of the enginesystem and recirculated exhaust gases) as it passes through CAC 40. Assuch, recirculated exhaust gases from first EGR passage 50 and/or secondEGR passage 58 may be cooled via CAC 40 before entering intake manifold44. In an alternative example, second EGR passage 58 may be coupled tointake passage 28 downstream of CAC 40. In such an example, there may beno EGR cooler 52 disposed within first EGR passage 50. Further, as shownin FIG. 1, a second ejector 57 may be positioned within intake passage28 at an outlet of second EGR passage 58.

A second (e.g., mid-pressure) EGR valve 59 is disposed within second EGRpassage 58. Second EGR valve 59 is configured to adjust an amount of gasflow (e.g., blowthrough air and/or exhaust) through second EGR passage58. As further described below, controller 12 may actuate EGR valve 59into an open (e.g., fully open) position (allowing minimally restrictedflow thorough second EGR passage 58), a closed (e.g., fully closed)position (blocking flow through second EGR passage 58), or plurality ofpositions between fully open and fully closed based on (e.g., as afunction of) engine operating conditions. For example, actuating EGRvalve 59 may include controller 12 sending an electronic signal to anactuator of EGR valve 59 to move a valve plate of EGR valve 59 into theopen position, the closed position, or some position between fully openand fully closed. Based on system pressures and positions of variousother valves in the engine system, air may either flow toward intakepassage 28 within second EGR passage 58 or toward second exhaustmanifold 80 within second EGR passage 58.

Intake passage 28 further includes an intake throttle 62. As shown inFIG. 1, intake throttle 62 is positioned downstream of CAC 40. Aposition of a throttle plate 64 of throttle 62 may be adjusted bycontroller 12 via a throttle actuator (not shown) communicativelycoupled to controller 12. By modulating intake throttle 62 whileoperating compressor 162, a desired amount of fresh air and/orrecirculated exhaust gas may be cooled by CAC 40 and delivered to theengine cylinders at a boosted pressure via intake manifold 44.

To reduce compressor surge, at least a portion of the air chargecompressed by compressor 162 may be recirculated to the compressorinlet. A compressor recirculation passage 41 may be provided forrecirculating compressed air from the compressor outlet, upstream of CAC40, to the compressor inlet. A compressor recirculation valve (CRV) 42may be provided for adjusting an amount of recirculation flowrecirculated to the compressor inlet. In one example, CRV 42 may beactuated open via a command from controller 12 in response to actual orexpected compressor surge conditions.

A third flow passage 30 (which may be referred to herein as a hot pipe)is coupled between second exhaust manifold 80 and intake passage 28.Specifically, a first end of third flow passage 30 is directly coupledto second exhaust manifold 80, and a second end of third flow passage 30is directly coupled to intake passage 28, downstream of intake throttle62 and upstream of intake manifold 44. A third valve 32 (e.g., a hotpipe valve) is disposed within third flow passage 30 and is configuredto adjust an amount of air flow through third flow passage 30. Thirdvalve 32 may be actuated into a fully open position, a fully closedposition, or a plurality of positions between fully open and fullyclosed in response to an actuation signal sent to an actuator of thirdvalve 32 from controller 12.

Second exhaust manifold 80 and/or second exhaust runners 82 may includeone or more sensors (such as pressure, oxygen, and/or temperaturesensors) disposed therein. For example, as shown in FIG. 1, secondexhaust manifold 80 includes a pressure sensor 34 and oxygen sensor 36disposed therein and configured to measure a pressure and oxygencontent, respectively, of exhaust gases and blowthrough (e.g., intake)air exiting second exhaust valves 6 and entering second exhaust manifold80. Additionally or alternatively to oxygen sensor 36, each secondexhaust runner 82 may include an individual oxygen sensor 38 disposedtherein. As such, an oxygen content of exhaust gases and/or blowthroughair exiting each cylinder via second exhaust valves 6 may be determinedbased on an output of oxygen sensors 38 and/or oxygen sensor 36.

In some examples, as shown in FIG. 1, intake passage 28 may include anelectric compressor 60. Electric compressor 60 is disposed in a bypasspassage 61, which is coupled to intake passage 28 upstream anddownstream of an electric compressor valve 63. Specifically, an inlet tobypass passage 61 is coupled to intake passage 28 upstream of electriccompressor valve 63, and an outlet to bypass passage 61 is coupled tointake passage 28 downstream of electric compressor valve 63 andupstream of where first EGR passage 50 couples to intake passage 28.Further, the outlet of bypass passage 61 is coupled upstream in intakepassage 28 from turbocharger compressor 162. Electric compressor 60 maybe electrically driven by an electric motor using energy stored at anenergy storage device. In one example, the electric motor may be part ofelectric compressor 60, as shown in FIG. 1. When additional boost (e.g.,increased pressure of the intake air above atmospheric pressure) isrequested over an amount provided by compressor 162, controller 12 mayactivate electric compressor 60 such that it rotates and increases apressure of intake air flowing through bypass passage 61. Further,controller 12 may actuate electric compressor valve 63 into a closed orpartially closed position to direct an increased amount of intake airthrough bypass passage 61 and electric compressor 60.

Intake passage 28 may include one or more additional sensors (such asadditional pressure, temperature, flow rate, and/or oxygen sensors). Forexample, as shown in FIG. 1, intake passage 28 includes a mass air flow(MAF) sensor 48 disposed upstream of electric compressor valve 63 inintake passage 28. An intake pressure sensor 31 and an intaketemperature sensor 33 are positioned in intake passage 28 upstream ofcompressor 162 and downstream of where first EGR passage 50 couples tointake passage 28. An intake oxygen sensor 35 may be located in intakepassage 28 downstream of compressor 162 and upstream of CAC 40. Anadditional intake pressure sensor 37 may be positioned in intake passage28 downstream of CAC 40 and upstream of throttle 62. In some examples,as shown in FIG. 1, an additional intake oxygen sensor 39 may bepositioned in intake passage 28 between CAC 40 and throttle 62. Further,an intake manifold pressure (e.g., MAP) sensor 122 and an intakemanifold temperature sensor 123 are positioned within intake manifold44, upstream of the engine cylinders.

In some examples, engine 10 may be coupled to an electric motor/batterysystem (as shown in FIG. 2) in a hybrid vehicle. The hybrid vehicle mayhave a parallel configuration, a series configuration, or variations orcombinations thereof. Further, in some examples, other engineconfigurations may be employed, for example a diesel engine.

Engine 10 may be controlled at least partially by control system 17,including controller 12, and by input from a vehicle operator via aninput device (not shown in FIG. 1). Control system 17 is shown receivinginformation from a plurality of sensors 16 (various examples of whichare described herein) and sending control signals to a plurality ofactuators 83. As one example, sensors 16 may include the pressure,temperature, and oxygen sensors located within intake passage 28, intakemanifold 44, exhaust passage 74, and second exhaust manifold 80described above. Other sensors may include a throttle inlet temperaturesensor for estimating a throttle air temperature (TCT) coupleddownstream of throttle 62 in the intake passage. Additional systemsensors and actuators are elaborated below with reference to FIG. 2. Asanother example, actuators 83 may include fuel injectors 66, valves 63,42, 54, 59, 32, 97, 76, and throttle 62. Actuators 83 may furtherinclude various camshaft timing actuators coupled to the cylinder intakeand exhaust valves (as described below with reference to FIG. 2).Controller 12 may receive input data from the various sensors, processthe input data, and trigger the actuators in response to the processedinput data based on instruction or code programmed in a memory ofcontroller 12 corresponding to one or more routines. An example controlroutine (e.g., method) is described herein at FIG. 7. For example, atotal flow through a scavenge EGR passage and individual concentrationsof constituents within the total flow may be determined based on thevalve overlap between the scavenge valve and intake valves, the valveoverlap determined based on intake and exhaust cam timings. Thecontroller may then adjust an engine operating parameter, such aposition of one or more valves and exhaust and/or intake cam timings,based on the determined total flow and concentrations of constituentsthrough the scavenge EGR passage.

It should be noted that while FIG. 1 shows engine 10 including each offirst EGR passage 50, second EGR passage 58, flow passage 98, and flowpassage 30, in other examples, engine 10 may only include a portion ofthese passages. For example, engine 10 may only include first EGRpassage 50 and flow passage 98 and not include second EGR passage 58 andflow passage 30. In another example, engine 10 may include first EGRpassage 50, second EGR passage 58, and flow passage 98, but not includeflow passage 30. In yet another example, engine 10 may include first EGRpassage 50, flow passage 30, and flow passage 98, but not second EGRpassage 58. In some examples, engine 10 may not include electriccompressor 60. In still other examples, engine 10 may include all oronly a portion of the sensors shown in FIG. 1.

Referring now to FIG. 2, a partial view of a single cylinder of internalcombustion engine 10 is shown. As such, components previously introducedin FIG. 1 are represented with the same reference numbers and are notre-introduced. Engine 10 is depicted with combustion chamber (cylinder)130, which may represent any of cylinders 13, 14, 15, and 18 of FIG. 1.Combustion chamber 130 includes a coolant sleeve 114 and cylinder walls132, with a piston 136 positioned therein and connected to a crankshaft140. Combustion chamber 130 is shown communicating with intake manifold44 and first exhaust port 86 via intake valve 4 and first exhaust valve8, respectively. As previously described in FIG. 1, each cylinder ofengine 10 may exhaust combustion products along two conduits, and onlythe first exhaust port (e.g., runner) leading from the cylinder to theturbine is shown in FIG. 2, while the second exhaust port (e.g., secondexhaust port 82) is not visible in this view.

As also previously elaborated in FIG. 1, each cylinder of engine 10 mayinclude two intake valves and two exhaust valves. In the depicted view,only one intake valve (e.g., intake valve 4) and first exhaust valve 8are shown. Intake valve 4 and first exhaust valve 8 are located at anupper region of combustion chamber 130. Intake valve 4 and first exhaustvalve 8 may be controlled by controller 12 using respective camactuation systems including one or more cams. The cam actuation systemsmay utilize one or more of cam profile switching (CPS), variable camtiming (VCT), variable valve timing (VVT), and/or variable valve lift(VVL) systems to vary valve operation. In the depicted example, eachintake valve, including intake valve 4, is controlled by an intake cam151, and each exhaust valve, including first exhaust valve 8, iscontrolled by an exhaust cam 153. The intake cam 151 may be actuated viaan intake valve timing actuator 101 and the exhaust cam 153 may beactuated via an exhaust valve timing actuator 103 according to setintake and exhaust valve timings, respectively. In some examples, theintake valves and exhaust valves may be deactivated via the intake valvetiming actuator 101 and exhaust valve timing actuator 103, respectively.For example, the controller may send a signal to the exhaust valvetiming actuator 103 to deactivate the first exhaust valve 8 such that itremains closed and does not open at its set timing. The position ofintake camshaft 151 and exhaust camshaft 153 may be determined bycamshaft position sensors 155 and 157, respectively. As introducedabove, in one example, all exhaust valves of every cylinder may becontrolled on a same exhaust camshaft. As such, a timing of both of thescavenge (second) exhaust valve and the blowdown (first) exhaust valvemay be adjusted together via one camshaft, but they may each havedifferent timings relative to one another. In another example, theblowdown exhaust valve of every cylinder may be controlled via a firstexhaust camshaft, and a scavenge exhaust valve of every cylinder may becontrolled on via different, second exhaust camshaft. In this way, thevalve timing of the scavenge valves and blowdown valves may be adjustedseparately from one another. In alternative examples, the cam or valvetiming system(s) of the scavenge and/or blowdown exhaust valves mayemploy a cam in cam system, an electrohydraulic-type system on thescavenge valves, and/or an electro-mechanical valve lift control on thescavenge valves.

In some examples, the intake and/or exhaust valves may be controlled byelectric valve actuation. For example, cylinder 130 may alternativelyinclude an intake valve controlled via electric valve actuation and anexhaust valve controlled via cam actuation, including CPS and/or VCTsystems. In still other examples, the intake and exhaust valves may becontrolled by a common valve actuator or actuation system or a variablevalve timing actuator or actuation system. In one example, intake cam151 includes separate and different cam lobes that provide differentvalve profiles (e.g., valve timing, valve lift, duration, etc.) for eachof the two intake valves of combustion chamber 130. Likewise, exhaustcam 153 may include separate and different cam lobes that providedifferent valve profiles (e.g., valve timing, valve lift, duration,etc.) for each of the two exhaust valves of combustion chamber 130. Inanother example, intake cam 151 may include a common lobe, or similarlobes, that provide a substantially similar valve profile for each ofthe two intake valves.

In addition, different cam profiles for the different exhaust valves canbe used to separate exhaust gases exhausted at lower cylinder pressuresfrom exhaust gases exhausted at higher cylinder pressures. For example,a first exhaust cam profile can open the first exhaust valve (e.g.,blowdown valve) from a closed position just before bottom dead center(BDC) of the power stroke of combustion chamber 130 and close the sameexhaust valve well before top dead center (TDC) of the exhaust stroke toselectively exhaust blowdown gases from the combustion chamber. Further,a second exhaust cam profile can be used to open the second exhaustvalve (e.g., scavenge valve) from a closed position before a mid-pointof the exhaust stroke and close it after TDC to selectively exhaust thescavenging portion of the exhaust gases. Example valve timings will bedescribed below with respect to FIG. 3.

Thus, the timing of the first exhaust valve and the second exhaust valvecan isolate cylinder blowdown gases from a scavenging portion of exhaustgases while any residual exhaust gases in the clearance volume of thecylinder can be cleaned out with fresh intake air blowthrough duringpositive valve overlap between the intake valve and the scavenge exhaustvalves. By flowing a first portion of the exhaust gas leaving thecylinders (e.g., higher pressure exhaust) to the turbine (e.g., turbine165 introduced in FIG. 1) and a higher pressure exhaust passage andflowing a later, second portion of the exhaust gas (e.g., lower pressureexhaust) and blowthrough air to the compressor inlet (e.g., an inlet ofcompressor 162 introduced in FIG. 1), the engine system efficiency maybe increased.

Cylinder 130 can have a compression ratio, which is a ratio of volumeswhen piston 136 is at bottom dead center to top dead center.Conventionally, the compression ratio is in a range of 9:1 to 10:1.However, in some examples where different fuels are used, thecompression ratio may be increased. This may happen, for example, whenhigher octane fuels or fuels with higher latent enthalpy of vaporizationare used. The compression ratio may also be increased if directinjection is used due to its effect on engine knock.

In some examples, each cylinder of engine 10 may include spark plug 92for initiating combustion. Ignition system 88 can provide an ignitionspark to combustion chamber 130 via spark plug 92 in response to a sparkadvance signal SA from controller 12, under select operating modes.However, in some examples, spark plug 92 may be omitted, such as whereengine 10 initiates combustion by auto-ignition or by injection of fuel,such as when engine 10 is a diesel engine.

As a non-limiting example, cylinder 130 is shown including one fuelinjector 66. Fuel injector 66 is shown coupled directly to combustionchamber 130 for injecting fuel directly therein in proportion to a pulsewidth of a signal FPW received from controller 12 via an electronicdriver 168. In this manner, fuel injector 66 provides what is known asdirect injection (hereafter also referred to as “DI”) of fuel intocylinder 130. While FIG. 2 shows injector 66 as a side injector, it mayalso be located overhead of the piston, such as near the position ofspark plug 92. Such a position may increase mixing and combustion whenoperating the engine with an alcohol-based fuel due to the lowervolatility of some alcohol-based fuels. Alternatively, the injector maybe located overhead and near the intake valve to improve mixing. Inanother example, injector 66 may be a port injector providing fuel intothe intake port upstream of cylinder 130.

Fuel may be delivered to fuel injector 66 from a high pressure fuelsystem 180 including one or more fuel tanks, fuel pumps, and a fuelrail. Alternatively, fuel may be delivered by a single stage fuel pumpat a lower pressure. Further, while not shown, the fuel tanks mayinclude a pressure transducer providing a signal to controller 12. Fueltanks in fuel system 180 may hold fuel with different fuel qualities,such as different fuel compositions. These differences may includedifferent alcohol content, different octane, different heats ofvaporization, different fuel blends, and/or combinations thereof, etc.In some examples, fuel system 180 may be coupled to a fuel vaporrecovery system including a canister for storing refueling and diurnalfuel vapors. The fuel vapors may be purged from the canister to theengine cylinders during engine operation when purge conditions are met.

Engine 10 may be controlled at least partially by controller 12 and byinput from a vehicle operator 113 via an accelerator pedal 116 and anaccelerator pedal position sensor 118 and via a brake pedal 117 and abrake pedal position sensor 119. The accelerator pedal position sensor118 may send a pedal position signal (PP) to controller 12 correspondingto a position of accelerator pedal 116, and the brake pedal positionsensor 119 may send a brake pedal position (BPP) signal to controller 12corresponding to a position of brake pedal 117. Controller 12 is shownin FIG. 3 as a microcomputer, including a microprocessor unit 102,input/output ports 104, an electronic storage medium for executableprograms and calibration values shown as a read only memory 106 in thisparticular example, random access memory 108, keep alive memory 110, anda data bus. Storage medium read-only memory 106 can be programmed withcomputer readable data representing instructions executable bymicroprocessor 102 for performing the methods and routines describedbelow as well as other variants that are anticipated but notspecifically listed. Controller 12 may receive various signals fromsensors coupled to engine 10, in addition to those signals previouslydiscussed, including a measurement of inducted mass air flow (MAF) frommass air flow sensor 48, an engine coolant temperature signal (ECT) froma temperature sensor 112 coupled to coolant sleeve 114, a profileignition pickup signal (PIP) from a Hall effect sensor 120 (or othertype) coupled to crankshaft 140, a throttle position (TP) from athrottle position sensor coupled to throttle 62, and an absolutemanifold pressure signal (MAP) from MAP sensor 122. An engine speedsignal, RPM, may be generated by controller 12 from signal PIP. Themanifold pressure signal MAP from the manifold pressure sensor may beused to provide an indication of vacuum or pressure in the intakemanifold.

Based on input from one or more of the above-mentioned sensors,controller 12 may adjust one or more actuators, such as fuel injector66, throttle 62, spark plug 92, intake/exhaust valves and cams, etc. Thecontroller may receive input data from the various sensors, process theinput data, and trigger the actuators in response to the processed inputdata based on instruction or code programmed therein corresponding toone or more routines, an example of which is described herein withrespect to FIG. 7.

In some examples, the vehicle may be a hybrid vehicle with multiplesources of torque available to one or more vehicle wheels 160. In otherexamples, the vehicle is a conventional vehicle with only an engine. Inthe example shown in FIG. 2, the vehicle includes engine 10 and anelectric machine 161. Electric machine 161 may be a motor or amotor/generator and thus may also be referred to herein as an electricmotor. Electric machine 161 receives electrical power from a tractionbattery 170 to provide torque to vehicle wheels 160. Electric machine161 may also be operated as a generator to provide electrical power tocharge battery 170, for example during a braking operation.

Crankshaft 140 of engine 10 and electric machine 161 are connected via atransmission 167 to vehicle wheels 160 when one or more clutches 166 areengaged. In the depicted example, a first clutch 166 is provided betweencrankshaft 140 and electric machine 161, and a second clutch 166 isprovided between electric machine 161 and transmission 167. Controller12 may send a signal to an actuator of each clutch 166 to engage ordisengage the clutch, so as to connect or disconnect crankshaft 140 fromelectric machine 161 and the components connected thereto, and/orconnect or disconnect electric machine 161 from transmission 167 and thecomponents connected thereto. Transmission 167 may be a gearbox, aplanetary gear system, or another type of transmission. The powertrainmay be configured in various manners including as a parallel, a series,or a series-parallel hybrid vehicle.

Now turning to FIG. 3, graph 300 depicts example valve timings withrespect to a piston position for an engine cylinder comprising fourvalves: two intake valves and two exhaust valves, such as describedabove with reference to FIGS. 1 and 2. The cylinder is configured toreceive intake air via the two intake valves (e.g., intake valves 2 and4 introduced in FIG. 1), exhaust a first, blowdown portion of exhaustgas to a turbine inlet via a blowdown exhaust valve (e.g., first, orblowdown, exhaust valve 8 introduced in FIG. 1), exhaust a second,scavenging portion of exhaust gas to an intake passage via a scavengeexhaust valve (e.g., second, or scavenge, exhaust valve 6 introduced inFIG. 1), and provide non-combusted blowthrough air to the intake passagevia the scavenge exhaust valve. By adjusting the timing of the openingand/or closing of the scavenge exhaust valve with that of the two intakevalves, residual exhaust gases in the cylinder clearance volume may beflushed out and recirculated as EGR along with fresh intake blowthroughair.

Graph 300 illustrates an engine position along the horizontal axis incrank angle degrees (CAD). In the example of FIG. 3, relativedifferences in timings can be estimated by the drawing dimensions.However, other relative timings may be used, if desired. Plot 302depicts piston position (along the vertical axis) relative to top deadcenter (TDC), bottom dead center (BDC), and the four strokes of anengine cycle (intake, compression, power, and exhaust). During theintake stroke, generally, the exhaust valves close and intake valvesopen. Air is introduced into the cylinder via the intake manifold andthe corresponding intake ports, and the piston moves to the bottom ofthe cylinder so as to increase the volume within the cylinder. Theposition at which the piston is at its bottom-most position in thecylinder and at the end of its stroke (e.g., when the combustion chamberis at its largest volume) is typically referred to as BDC. During thecompression stroke, the intake valves and the exhaust valves are closed.The piston moves toward the cylinder head so as to compress the airwithin the cylinder. The point at which the piston is at the end of itsstroke and closest to the cylinder head (e.g., when the combustionchamber is at its smallest volume) is typically referred to as TDC. In aprocess herein referred to as injection, fuel is introduced into thecombustion chamber. In a process herein referred to as ignition, theinjected fuel is ignited, such as via a spark from a spark plug,resulting in combustion. During the expansion stroke, the expandinggases push the piston back down to BDC. A crankshaft (e.g., crankshaft140 shown in FIG. 2) converts this piston movement into a rotationaltorque of the rotary shaft. During the exhaust stroke, the exhaustvalves are opened to release the combusted air-fuel mixture to thecorresponding exhaust passages, and the piston returns to TDC. In thisdescription, the second exhaust (scavenge) valves may be opened afterthe beginning of the exhaust stroke and may stay open until after theend of the exhaust stroke, while the first exhaust (blowdown) valves areclosed and the intake valves are opened to flush out residual exhaustgases with blowthrough air.

Plot 304 depicts an intake valve timing, lift, and duration for a firstintake valve (Int_1), while plot 306 depicts an intake valve timing,lift, and duration for a second intake valve (Int_2), both intake valvescoupled to the intake passage of the engine cylinder. Plot 308 depictsan example exhaust valve timing, lift, and duration for a blowdownexhaust valve (Exh_1), which may correspond to first (e.g., blowdown)exhaust valve 8 introduced in FIG. 1, coupled to a first exhaustmanifold (e.g., blowdown exhaust manifold 84 shown in FIG. 1) of via afirst exhaust port (e.g., first exhaust port 86 of FIG. 1). Plot 310depicts an example exhaust valve timing, lift, and duration for ascavenge exhaust valve (Exh_2), which may correspond to second (e.g.,scavenge) exhaust valve 6 shown in FIG. 1, coupled to a scavengemanifold (e.g., scavenge manifold 80 shown in FIG. 1) via a secondexhaust port (e.g., second exhaust port 82 of FIG. 1). As previouslyelaborated, the first exhaust manifold connects (e.g., fluidly couples)the blowdown exhaust valve to the inlet of a turbocharger turbine (e.g.,turbine 165 of FIG. 1), and the scavenge manifold connects (e.g.,fluidly couples) the scavenge exhaust valve to an intake passage via anEGR passage (e.g., first EGR passage 50 shown in FIG. 1). The firstexhaust manifold may be separate from the scavenge manifold, asexplained above.

In the depicted example, the first and second intake valves are fullyopened from a closed position (e.g., a valve lift of zero) at a commontiming (plots 304 and 306), beginning near the intake stroke TDC justafter CAD2 (e.g., at or just after the intake stroke TDC), and areclosed after a subsequent compression stroke has commenced past CAD3(e.g., after BDC). Additionally, when opened fully, the two intakevalves may be opened with a same amount of valve lift L1 for a sameduration of D1. In other examples, the two intake valves may be operatedwith a different timing by adjusting the phasing, lift, or duration. Incontrast to the common timing of the first and second intake valves, thetiming of the blowdown exhaust valve opening and closing may bestaggered relative to the scavenge exhaust valve opening and closing.Specifically, the blowdown exhaust valve (plot 308) is opened from aclosed position at a first timing that is earlier in the engine cyclethan the timing at which the scavenge exhaust valve (plot 310) is openedfrom a closed position. Specifically, the first timing for opening theblowdown exhaust valve is between TDC and BDC of the power stroke,before CAD1 (e.g., before the exhaust stroke BDC), while the timing foropening the scavenge exhaust valve is just after the exhaust stroke BDC,after CAD1 but before CAD2. The blowdown exhaust valve (plot 308) isclosed before the end of the exhaust stroke, and the scavenge exhaustvalve (plot 310) is closed after the end of the exhaust stroke. Thus,the scavenge exhaust valve remains open to overlap slightly with openingof the intake valves.

To elaborate, the blowdown exhaust valve (plot 308) may be fully openedfrom close before the start of an exhaust stroke (e.g., between 90 and30 degrees before BDC, depending on cam phasing), maintained fully openthrough a first part of the exhaust stroke, and may be fully closedbefore the exhaust stroke ends (e.g., between 50 and 0 degrees beforeTDC, depending on cam phasing) to collect the blowdown portion of theexhaust pulse. The scavenge exhaust valve (plot 310) may be fully openedfrom a closed position just after the beginning of the exhaust stroke(e.g., between 30 and 90 degrees past BDC, depending on cam phasing),maintained open through a second portion of the exhaust stroke, and maybe fully closed after the intake stroke begins (e.g., between 20 and 70degrees after TDC, depending on cam phasing) to exhaust the scavengingportion of the exhaust. Additionally, the scavenge exhaust valve and theintake valves, as shown in FIG. 3, may have a positive overlap phase(e.g., from between 20 degrees before TDC and 30 degrees after TDC untilbetween 30 and 90 degrees past TDC, depending on cam phasing) to allowblowthrough with EGR. This cycle, wherein all four valves areoperational, may repeat itself based on engine operating conditions.

Additionally, the blowdown exhaust valve (plot 308) may be opened with afirst amount of valve lift L2, while the scavenge exhaust valve (plot310) may be opened with a second amount of valve lift L3, where L3 issmaller than L2. Further still, the blowdown exhaust valve may be openedat the first timing for a duration D2, while the scavenge exhaust valvemay be opened for a duration D3, where D3 is smaller than D2. It will beappreciated that in other examples, the two exhaust valves may have thesame amount of valve lift and/or same duration of opening while openingat differently phased timings.

In this way, by using staggered valve timings, engine efficiency andpower can be increased by separating exhaust gases released at higherpressure (e.g., expanding blowdown exhaust gases in the cylinder) fromresidual exhaust gases at low pressure (e.g., exhaust gases that remainin the cylinder after blowdown) into the different manifolds. Further,by conveying low pressure residual exhaust gases as EGR along withblowthrough air to the compressor inlet (via the first EGR passage andthe scavenge manifold), combustion chamber temperatures can be lowered,thereby reducing an occurrence of knock and an amount of spark retardfrom maximum brake torque timing. Further, because the exhaust gases atthe end of the exhaust stroke are directed to either downstream of theturbine or upstream of the compressor, which are both at lowerpressures, exhaust pumping losses can be minimized to increase engineefficiency.

Thus, exhaust gases can be used more efficiently than simply directingall the exhaust gas of a cylinder through a single, common exhaust portto the turbocharger turbine. As such, several advantages may beachieved. For example, the average exhaust gas pressure supplied to theturbocharger can be increased by separating and directing the blowdownpulse into the turbine inlet to increase turbocharger output.Additionally, fuel economy may be increased because blowthrough air isnot routed to the catalyst, being directed to the compressor inletinstead, and therefore, excess fuel may not be injected into the exhaustgases to maintain a stoichiometric air-fuel ratio upstream of thecatalyst.

However, a composition of the gas conveyed through the scavenge exhaustvalve to the compressor inlet (via the first EGR passage and thescavenge manifold) varies throughout the scavenge exhaust valve openduration and further varies based on operating parameters, such as aduration of the positive valve overlap phase between the scavengeexhaust valve and the intake valves, relative pressures of the intakemanifold and the scavenge manifold, and a timing of a fuel directinjection relative to a closing timing of the scavenge exhaust valve.Therefore, FIGS. 4A-4D schematically illustrate sources of differentrecirculated gases throughout an open duration of the scavenge exhaustvalve. Specifically, a cylinder diagram 400 in each of FIGS. 4A-4Dschematically depicts gas flow through the cylinder at an engineposition shown in a corresponding valve diagram 450. Components ofcylinder diagram 400 that are the same as the components shown in FIGS.1 and 2 are numbered the same and may not be reintroduced. Valve diagram450 shows engine position along the horizontal axis (in crank angledegrees after TDC of the intake stroke) and valve lift along thevertical axis (in millimeters). An example valve timing, lift, andduration for a set of intake valves is shown in plot 404 (e.g., intakevalves 2 and 4 introduced in FIG. 1 and shown in cylinder diagram 400),an example valve timing, lift, and duration for a first, blowdownexhaust valve is shown in plot 408 (e.g., blowdown exhaust valve 8introduced in FIG. 1 and shown in cylinder diagram 400), and an examplevalve timing, lift, and duration for a second, scavenge exhaust valve isshown in plot 410 (e.g., scavenge exhaust valve 6 introduced in FIG. 1and shown in cylinder diagram 400).

Turning first to FIG. 4A, cylinder diagram 400 shows gas flow throughscavenge exhaust valve 6 at a first engine position indicated by adashed line 416 on valve diagram 450. The first engine position occursduring an exhaust stroke, just before TDC of the intake stroke. Intakevalves 2 and 4 are closed at the first engine position, as indicated byblack filled circles for intake valves 2 and 4 in cylinder diagram 400and as shown by plot 404 in valve diagram 450. Blowdown exhaust valve 8is also substantially closed at the first engine position. Scavengeexhaust valve 6 is open at the first engine position, as indicated by awhite filled circle for scavenge exhaust valve 6 in cylinder diagram 400and as shown by plot 410 in valve diagram 450. With the intake valvesclosed, residual gases 414 from combustion (also referred to herein ascombustion products) that have not already exited the cylinder asblowdown exhaust (e.g., via blowdown exhaust valve 8) flow from cylinder130 through the open scavenge exhaust valve 6 and toward scavengemanifold 80 via second exhaust port 82. Further, with blowdown exhaustvalve 8 substantially closed at the first engine position, the residualgases 414 do not flow through the blowdown exhaust valve and towardfirst exhaust manifold 84 via first exhaust port 86. For example, ablowdown portion of residual gases 414 may have already been exhaustedthrough blowdown exhaust valve 8 earlier in the engine cycle (e.g., at amore negative crank angle with respect to TDC of the intake stroke)while blowdown exhaust valve 8 was open (e.g., as shown in plot 408).Residual gases (e.g., combustion gases) 414 may be comprised of burntgases, a mixture of burnt gases and air, and/or a mixture of burnt gasesand unburned hydrocarbons injected during the previous engine cycle, forexample.

Turning next to FIG. 4B, cylinder diagram 400 shows gas flow throughscavenge exhaust valve 6 at a second engine position indicated by adashed line 418 on valve diagram 450. The second engine position occursduring the intake stroke, shortly after TDC. Intake valves 2 and 4 areopen at the second engine position, as indicated by white filled circlesfor intake valves 2 and 4 in cylinder diagram 400 and as shown by plot404 in valve diagram 450. Blowdown exhaust valve 8 is fully closed atthe second engine position. Scavenge exhaust valve 6 remains open at thesecond engine position, as indicated by a white filled circle forscavenge exhaust valve 6 in cylinder diagram 400 and as shown by plot410 in valve diagram 450. With the intake valves open, pushback gases420 flow from intake ports 20 and 22, though the open intake valves 2and 4, through cylinder 130, through the open scavenge exhaust valve 6,and toward scavenge manifold 80 via second exhaust port 82. Further,with blowdown exhaust valve 8 fully closed at the second engineposition, the pushback gases 420 do not flow through the blowdownexhaust valve and toward first exhaust manifold 84 via first exhaustport 86. Pushback gases 420 may be comprised of a mixture of burntgases, air, and/or unburned hydrocarbons injected during the previousengine cycle. For example, while intake valves 2 and 4 are open, gas mayflow from cylinder 130 to intake ports 20 and 22 based on an in-cylinderpressure and a pressure in the intake ports (e.g., based on MAP) and mayremain in the intake ports upon intake valve closing. Further, an amountof unburned hydrocarbons in the pushback gases 420 varies based on anamount of overlap between a start of injection (SOI) of a fuel directinjection and a closing timing of scavenge exhaust valve 6. Then, duringa subsequent engine cycle, pushback gases 420 may flow from intake ports20 and 22 into cylinder 130 upon intake valve opening, and at least aportion of the pushback gases 420 may then flow through scavenge exhaustvalve 6 onto scavenge manifold 80.

Next, cylinder diagram 400 of FIG. 4C shows gas flow through scavengeexhaust valve 6 at a third engine position indicated by a dashed line422 on valve diagram 450. Intake valves 2 and 4 are open at the thirdengine position, as indicated by white filled circles for intake valves2 and 4 in cylinder diagram 400 and as shown by plot 404 in valvediagram 450. Blowdown exhaust valve 8 is fully closed at the thirdengine position. Scavenge exhaust valve 6 remains open at the thirdengine position, as indicated by a white filled circle for scavengeexhaust valve 6 in cylinder diagram 400 and as shown by plot 410 invalve diagram 450. Fuel is directly injected into cylinder 130 via fuelinjector 66 at the third engine position. With the scavenge exhaustvalve open, short-circuited (e.g., scavenged) fuel 424 from the fueldirect injection flows directly through scavenge exhaust valve 6 andtoward scavenge manifold 80 via second exhaust port 82. An amount of theshort-circuited fuel 424 varies based on an amount of overlap betweenthe SOI of the fuel direct injection and a closing timing of scavengeexhaust valve 6, an intake-to-scavenge manifold flow, a duration of thepositive overlap between intake valves 2 and 4 and scavenge exhaustvalve 6, an amount of flow through a scavenge manifold bypass passage(e.g., SMBP 98 shown in FIG. 1), an amount of fuel injected in the fueldirect injection, an end of injection (EOI) timing of the fuel directinjection, and a relative pressure between the scavenge manifold and theintake. That is, a portion of the directly injected fuel may flowthrough scavenge exhaust valve 6 as short-circuited fuel 242, with theportion varying (relative to a total amount of fuel directly injected)based on pressure and flow characteristics of the scavenge manifold andthe intake manifold and the amount of overlap between the directinjection and an open duration of scavenge exhaust valve 6.

In FIG. 4D, cylinder diagram 400 shows gas flow through scavenge exhaustvalve 6 at a fourth engine position indicated by a dashed line 426 onvalve diagram 450. Intake valves 2 and 4 are open at the fourth engineposition, as indicated by white filled circles for intake valves 2 and 4in cylinder diagram 400 and as shown by plot 404 in valve diagram 450.Blowdown exhaust valve 8 is fully closed at the fourth engine position.Scavenge exhaust valve 6 remains open at the fourth engine position, asindicated by a white filled circle for scavenge exhaust valve 6 incylinder diagram 400 and as shown by plot 410 in valve diagram 450. Withthe intake valves open, intake manifold gases 428 flow from intakemanifold 44, through intake ports 20 and 22 to the open intake valves 2and 4, through cylinder 130, through the open scavenge exhaust valve 6,and toward scavenge manifold 80 via second exhaust port 82. Further,with blowdown exhaust valve 8 fully closed at the fourth engineposition, the intake manifold gases 428 do not flow through the blowdownexhaust valve and toward first exhaust manifold 84 via first exhaustport 86. Intake manifold gases 428 may be comprised of fresh air,recirculated burnt gases (e.g., as recirculated by first EGR passage 50shown in FIG. 1), and, in some examples, recirculated (unburnt) fuel,for example. For example, fuel scavenged during a first engine cycle maybe recirculated through an EGR passage (e.g., first EGR passage 50 shownin FIG. 1) to intake manifold 44. Then, during a second, subsequentengine cycle, the fuel scavenged during the first engine cycle may flowfrom intake manifold 44 into cylinder 130. In some examples, at least aportion of the fuel scavenged during the first engine cycle may furtherflow through the open scavenge exhaust valve 6 during the second enginecycle as intake manifold gases 428.

Thus, FIGS. 4A-4D, show different sources of recirculated gasesthroughout the open duration of the second (e.g., scavenge) exhaustvalve. The different sources of recirculated gases may supply gases ofvarying composition, which may further vary based on scavenge valvetiming, intake valve timing, fuel injection timing, and pressure andflow characteristics. A timing of the intake valves, scavenge exhaustvalve, and thus the opening overlap between the intake valves andscavenge exhaust valve, affect the relative portions of residual gases(e.g., combustion gases), pushback gases, and intake manifold gases thatenter the scavenge exhaust manifold, as described further below withreference to FIGS. 5 and 6A-6B.

As explained above, estimating the amount of burnt gases, air (e.g.,fresh air), and unburned hydrocarbons flowing to the intake passage viathe EGR passage and scavenge exhaust manifold is difficult due to thesystem architecture and valve timings, which results in various portionsof gases pushed into the scavenge manifold at various times (asdescribed above with reference to FIGS. 4A-4D). In order to estimate theflow amounts of each of the recirculated constituents (air, fuel, andburnt gases) in the EGR passage (to the intake passage, upstream of thecompressor), first an estimate of the total bulk flow (e.g., flow of allgases, including burnt gases, air, and fuel) through the EGR passagefrom the scavenge manifold may be needed. Previously, this total flowmeasurement through the EGR passage and across the EGR valve (e.g., BTCCvalve 54 shown in FIG. 1) may be determined via a delta pressuremeasurement system (e.g., DPFE system) using a differential pressuresensor arranged across the EGR valve and an associated orifice (using arocket nozzle or venturi, for example). However, this measurement mayrequire a significant delta pressure across the orifice, which may limitengine performance at high load conditions. Thus, instead, the inventorsherein propose estimating the bulk flow through the EGR passage andacross the BTCC valve based on the valve opening overlap between theintake valves and scavenge exhaust valve and a pressure drop across theoverlap (e.g., a difference in pressure between the intake manifold andscavenge exhaust manifold). Then, by mapping a relationship betweenvalve opening overlap between the intake valves and scavenge exhaustvalve (e.g., the relative intake valve and scavenge valve timings) andthe relative mass fractions of intake gases, pushback gases, andcombustion products within the total bulk EGR flow, the flow amounts ofeach of burnt gases, fuel, and air through the EGR passage to the intakepassage, upstream of the compressor, may be determined. These values maythen be used for engine control. Details of this method are describedbelow with reference to FIG. 7.

Turning to FIG. 7, a method 700 is shown for determining total flowthrough a scavenge EGR passage (an EGR passage from a scavenge exhaustmanifold to an intake passage, upstream of a compressor) and relativeconcentrations of burnt gases, fuel, and air within the total flow. Inone embodiment, the scavenge EGR passage may be EGR passage 50 shown inFIG. 1, and the flow through the scavenge EGR passage may be referred toas the SC-EGR flow. Instructions for carrying out method 700 may beexecuted by a controller based on instructions stored on a memory of thecontroller and in conjunction with signals received from sensors of theengine system, such as the sensors described above with reference toFIGS. 1 and/or 2. The controller may employ engine actuators of theengine system to adjust engine operation, according to the methodsdescribed below.

Method 700 begins at 702, which includes estimating and/or measuringoperating conditions. Operating conditions may include, for example, abrake pedal position, an acceleration pedal position, operator torquedemand, ambient temperature and humidity, barometric pressure, enginespeed, engine load, engine temperature, mass air flow (MAF), intakemanifold pressure (MAP), intake manifold temperature, oxygen content ofintake air/exhaust gases at various points in the engine system, adesired air-fuel ratio (AFR), an actual AFR, a timing of the cylinderintake and exhaust valves, positions of various valves of the enginesystem (including the BTCC valve), a temperature and/or loading level ofone or more emission control devices, pressures in the exhaust system(e.g., exhaust manifolds, exhaust ports, and/or exhaust passages), etc.The operating conditions may be measured or inferred based on availabledata.

At 704, the method includes determining the timing of the intake valves(e.g., of intake valves 2, 4 shown in FIG. 1) and the timing of thescavenge exhaust valves (e.g., second exhaust valves 6 shown in FIG. 1).The valve timings may be determined in terms of engine position (e.g.,crank angle degrees). For example, the crank angle degrees at which theintake valves of a cylinder open and close may be determined, as well asthe crank angle degrees at which the scavenge exhaust valve of thecylinder opens and closes. The method at 704 may further includedetermining the opening overlap between the scavenge exhaust valve andintake valves for a cylinder (e.g., the SV-IV overlap). The SV-IVoverlap may be a number of crank angle degrees for which both the intakevalves and the corresponding scavenge exhaust valve for a cylinder areopen at the same time in a cylinder cycle. Additionally, the method at704 may include determining, based on the determined valve timings, thecurrent valve lift of each of the scavenge valve and the intake valves,for the current time in the engine cycle (e.g., at the current crankangle degree in the engine cycle). This information may be used todetermine the (e.g., instantaneous) valve overlap area between thescavenge valve and intake valves, as described further below at 708.

Method 700 continues to 706 to determine the intake manifold pressureand scavenge (exhaust) manifold pressure. In one embodiment, the intakemanifold and scavenge manifold pressures may be estimated based onadditional engine operating conditions, such as pressures and/or flowsupstream and/or downstream of the desired locations. In anotherembodiment, the intake manifold and scavenge manifold pressures may bemeasured. As one example, the intake manifold pressure may be estimatedand/or measured from an output of a pressure sensor arranged within theintake manifold (e.g., intake pressure sensor 37 shown in FIG. 1). Asanother example, the scavenge manifold pressure may be estimated and/ormeasured from an output of a pressure sensor arranged within thescavenge manifold (e.g., pressure sensor 34 arranged in second exhaustmanifold 80). When measuring the intake manifold pressure and scavengemanifold pressure, these pressure measurements may be obtained from thecorresponding pressure sensors via high-frequency sampling (e.g., onemillisecond or 5 degree sampling). Further, these pressure measurementsmay be crank angle aligned so that the current intake manifold pressureand scavenge manifold pressures at the current time in the engine cyclemay be obtained and used in conjunction with the current valve overlaparea at 708, as described further below.

At 708, the method includes determining the total flow (also referred toherein as total bulk flow) through the scavenge EGR passage, from thescavenge manifold to the intake passage, upstream of the compressor,using the determined valve timings (determined at 704, and used todetermine the valve overlap area between the scavenge valve and intakevalves) and the determined pressures (determined at 706) at a currenttime in the engine cycle. A cylinder, between the intake valves andscavenge exhaust valve, may be modeled as a variable orifice device thatcontrols the flow through the cylinder and into the scavenge manifoldusing the relative openings between the scavenge exhaust valve andintake valves (of the cylinder) during the SV-IV overlap period (wherethe intake valves and scavenge valve of a cylinder are all at leastpartially open). The flow rate through this “orifice”, and thus into thescavenge manifold, may be related to the flow area (e.g., overlap areabetween the intake valves and scavenge valve) of the orifice using astandard orifice equation. An example of such an orifice equation, usedto determine total flow across an orifice (in this case, considered tobe between the scavenge valve and the corresponding intake valves), ispresented by the equations below.

$\begin{matrix}{\mspace{79mu} {{Q_{{SV} - {IV}} = {{g_{1}\left( {P_{IM},P_{SM}} \right)}{g_{2}(\theta)}}},}} & \left( {{Equation}\mspace{14mu} 1} \right) \\{{{g_{1}\left( {P_{IM},P_{SM}} \right)} = {\frac{A_{{SV} - {IV}}P_{SM}}{\sqrt{R_{air}T_{IM}}}\left( \frac{P_{IM}}{P_{SM}} \right)^{\frac{1}{\gamma}}\sqrt{\frac{2\; \gamma}{\gamma - 1}\left\lbrack {1 - \left( \frac{P_{IM}}{P_{SM}} \right)^{\frac{\gamma - 1}{\gamma}}} \right\rbrack}}},} & \left( {{Equation}\mspace{14mu} 2} \right) \\{\mspace{79mu} {{{g_{2}(\theta)} = {C_{D}(\theta)}},}} & \left( {{Equation}\mspace{14mu} 3} \right)\end{matrix}$

where Q_(SV-IV) is the total flow through the cylinder, from the intakevalves to the scavenge valve, which may be assumed to be the total bulkflow through the scavenge EGR passage. In the above equations, P_(IM) isthe intake manifold pressure, P_(SM) is the scavenge manifold pressure,and θ is the relative opening angle between the intake valve andscavenge valve (e.g., fraction or percentage opening overlap out of atotal amount of possible overlap between the intake valves and scavengevalve). In Equation 2, A_(SV-IV) is the valve overlap area between theintake valves and the scavenge valve (which is a function of the valvelift profiles for the intake valves and scavenge valves at the currentcrank angle), R_(air) is the universal gas constant of air, T_(IM) isthe temperature in the intake manifold, and γ is the specific weight ofthe gases. In Equation 3, C_(D)(θ) is an angle dependent dischargecoefficient. The multiplication of area and discharge coefficientprovide an equivalent effect to the valve overlap factor. Thus, using anorifice equation, such as those presented above in Equations 1-3, thedetermined intake manifold and scavenge manifold pressures at thecurrent crank angle, and the valve overlap area at the current crankangle, the current flow through the scavenge EGR passage may bedetermined. This total bulk flow amount may change over time, as thepressures and valve overlap area changes.

In one embodiment, the method at 708 may additionally include, at 710,filtering out an effect of pulsation on scavenge manifold pressure andestimating a transport delay in the determined total flow through thescavenge EGR passage based on engine speed. For example, as engine speedincreases, the amount of pulsations in the flow may also increase. Thus,a relationship between engine speed and scavenge manifold pressurepulsations may be determined (e.g., from engine mapping/modeling) andstored in the memory of the controller as a look-up table ormathematical relationship, where engine speed in the input, and acorrection to the determined (e.g., measured) scavenge manifold pressureis the output. Thus, based on a determined engine speed (e.g., estimatedand/or measured from one or more engine sensors), the controller mayinput the engine speed into the stored look-up table or relationship andreceive a scavenge manifold pressure correction as the output. Thecontroller may then correct the measured or estimated scavenge manifoldpressure using the determined correction and use the corrected scavengemanifold pressure in the orifice equation to determine the total bulkflow through the scavenge EGR passage, as described above. Similarly, atransport delay may be determined based on a measured and/or estimatedengine speed and used to adjust or update the determined total bulk flowthrough the scavenge EGR passage.

Continuing to 712, the method includes determining scavenge manifoldmass fractions of scavenge manifold gas portions based on the valveopening overlap between the scavenge valve and intake valves. Thescavenge manifold gas portions (e.g., portions of gases expelled intothe scavenge manifold and recirculated to the intake passage via thescavenge EGR passage, as described above with reference to FIGS. 4A-4D)include pushback gases (e.g., pushback gases 420 shown in FIG. 4B),combustion products (e.g., residual gases 414 shown in FIG. 4A), andintake manifold gases (e.g., intake manifold gases 428 shown in FIG.4D). While not explicitly shown in the breakdown of FIG. 5, the impactof short-circuiting of direct injected (DI) fuel on the fuelconcentration in the scavenge manifold may be mapped in a similarfashion to the other sources of scavenged fuel without loss ofgenerality.

A map (e.g., relationship) between the scavenge manifold mass fractionsof the scavenge manifold gas portions and intake valve to scavenge valveoverlap (e.g., amount of valve opening overlap between the intake valvesand scavenge valve) may be determined via engine mapping across a rangeof cam timings which result in various amounts of valve overlap betweenthe intake valves and scavenge valve (e.g., from a minimum amount ofpossible overlap to a maximum amount of possible overlap, based on thecam timing setups). For example, for varying intake and exhaust camtimings, the relative fractions of each of the scavenge manifold gasportions may be determined using engine mapping utilizing mass fractionbalance relationships.

An example map of the relationship between the scavenge manifold massfractions and the intake valve to scavenge valve overlap is shown inFIG. 5. Specifically, FIG. 5 shows a map 500 with scavenge manifold massfractions on the y-axis (from 0 to 1) and intake valve to scavenge valveoverlap (e.g., amount of positive valve overlap between the intakevalves and scavenge valve) on the x-axis (from a minimum amount ofopening overlap to a maximum amount of opening overlap). The scavengemanifold mass fractions are of the scavenge manifold gas portions whichinclude intake gases 502, pushback gases 504, and combustion products506. For each amount of intake valve to scavenge valve overlap, the sumof all the scavenge manifold mass fractions of each of the scavengemanifold gas portions equal one (e.g., 100%). As explained above, therange of intake valve to scavenge valve overlap shown on the x-axis ofmap 500 includes a range from a minimal amount of opening overlap to amaximal amount of opening overlap. Example valve timing diagrams for theextreme amounts (e.g., minimal and maximal) of valve overlap are shownin FIGS. 6A-6B. In each of FIGS. 6A-6B, which are similar to valvediagrams 450 shown in FIGS. 4A-4D, engine position is shown along thehorizontal axis (in crank angle degrees after TDC of the intake stroke)and valve lift is shown along the vertical axis (in millimeters). Anexample valve timing, lift, and duration for a set of intake valves isshown in plot 404 (e.g., intake valves 2 and 4 introduced in FIG. 1), anexample valve timing, lift, and duration for a first, blowdown exhaustvalve is shown in plot 408 (e.g., blowdown exhaust valve 8 introduced inFIG. 1), and an example valve timing, lift, and duration for a second,scavenge exhaust valve (e.g., scavenge valve) is shown in plot 410(e.g., scavenge exhaust valve 6 introduced in FIG. 1). In FIG. 6A, theexhaust cam is retarded, causing the scavenge valve timing to be moreretarded, and resulting in less valve overlap between the scavenge valveand intake valves (valve overlap area shown at 602). In FIG. 6B, theexhaust cam is advanced, causing the scavenge valve timing to be moreadvanced, and resulting in more valve overlap between the scavenge valveand intake valves (valve overlap area shown at 604).

Returning to FIG. 5, as seen in map 500, at a relatively low amount ofintake valve to scavenge valve overlap (the far left bar of map 500),the majority of the scavenge manifold gases are comprised of combustionproducts, with a small amount of intake gases. This is due to the intakevalves only being open for a relatively smaller amount of time beforethe scavenge valve closes. As the amount of intake valve to scavengevalve overlap increases, the relative fraction of combustion productsdecreases, while the relative fraction of intake gases increases. Thepushback gas fraction is slightly higher at the smaller valve overlaps,but does not change as drastically as overlap amount changes (ascompared to the intake gases and combustion products).

Returning to 712 of FIG. 7, a map of scavenge manifold mass fractions ofscavenge manifold gas portions vs. the amount of intake valve toscavenge valve overlap, such as the map shown in FIG. 5, may be storedin the memory of the controller as a map, look-up table, or mathematicalrelationship. Then, based on the set intake and exhaust cam timings(e.g., intake valve and scavenge valve timings), the amount of valveoverlap may be determined and input into the stored map, look-up table,or relationship. The controller may then receive the output of thescavenge manifold mass fractions for each of the scavenge manifold gasportions.

The method continues to 714 to determine the final burnt gas, fuel, andair (e.g., fresh air) concentrations in the recirculated scavenge EGRflow based on the determined mass fractions and assumed fractions ofconstituents in each scavenge manifold gas portion. As explained above,with reference to FIGS. 4A-4D, the combustion products may be comprisedof burnt gases, burnt gases and air, and burnt gases and unburnedhydrocarbons, the pushback gases may be comprised of air, burnt gas, andfuel, and the intake gases (e.g., intake manifold gases) may becomprised of fresh air, recirculated burnt gases, and recirculated(unburnt) fuel. In one embodiment, the fractions of fuel, burnt gases,and air in the pushback gases may be known for one or more of thescavenge manifold gas portions and determined according to a measured ortarget air-fuel ratio for combustion. If the composition of the pushbackgases can not be measured during a mapping exercise, then it will benecessary to make assumptions regarding its composition based onoperating condition. As for the fractions of the constituents in each ofthe intake gases and combustion products, these may be measured during amapping exercise and included in the engine strategy via mapping. Then,based on the determined mass fraction for each of the scavenge manifoldgas portion (e.g., pushback, combustion products, and intake gases) andthe assumed or determined fractions of constituents (e.g., burnt gas,fuel, and air) within each of the scavenge manifold portions, the finalconcentrations of burnt gas, fuel and air in the recirculated scavengeEGR flow may be determined.

At 716, the method includes determining the total flow of burnt gas,fuel, and air to the intake passage (upstream of the compressor) via thescavenge EGR passage based on the determined final burnt gas, fuel, andair concentrations and the determined total bulk flow through thescavenge EGR passage. For example, by multiplying the concentration ofeach of the final burnt gas, fuel, and air concentrations by the totalbulk flow (determined at 708), the total flows of each of burnt gas,fuel, and air recirculated to the intake passage via the scavenge EGRpassage may be determined. In this way, the method at 716 may determinethe relative amounts of burnt gases, fresh air, and unburnedhydrocarbons flowing to the intake passage, upstream of the compressor,via the scavenge manifold and scavenge EGR passage system.

Continuing to 718, the method includes adjusting engine operatingparameter(s) based on the determined total flows of burnt gas, fuel, andair. Adjusting the engine operating parameter(s) may include adjustingone or more of intake cam timing, exhaust cam timing (e.g., the timingof the scavenge exhaust valves), an amount of opening or position of theBTCC valve (e.g., valve 54 shown in FIG. 1), an amount of opening orposition of the scavenge manifold bypass valve (e.g., valve 97 shown inFIG. 1), an amount or timing of fuel injection into engine cylinders,etc. For example, based on the determined total flows of burnt gas,fuel, and air, the controller may determine a control signal to send toone or more of the valves listed above and/or the cam systems listedabove, such as a valve position or timing. As an example, the controllermay determine the valve adjustment or cam timing adjustment through adetermination that directly takes into account the determined totalflows of burnt gas, fuel, and air. In one example, this may includeincreasing the amount of opening of the BTCC valve as the total flow ofburnt gas decreases relative to a desired flow amount. The desired flowamount may be determined based on engine operating conditions, such asengine speed and/or load, mass air flow, etc. In other examples, thecontroller may determine the valve positions and/or cam timings based ona calculation using a look-up table with the inputs being the determinedtotal flows of burnt gas, fuel, and air, and the output(s) being a valveposition and/or cam timing adjustment. As another example, thecontroller may make a logical determination (e.g., regarding a positionof one or more of the above described valves or timing of the camsystem(s)) based on logic rules that are a function of the total flowsof the burnt gas, fuel, and air. The controller may then generate acontrol signal that is sent to an actuator of the valve(s) and/orcamshaft timing system(s). As one example, the controller may adjust aposition of the BTCC valve and/or exhaust cam timing in response to thedetermined total flow of burnt gases in order to achieve a desiredrecirculation of exhaust gases to the intake via the scavenge EGRpassage. For example, if the determined total flow of burnt gases islower than the desired recirculation of exhaust gases to the intake, thecontroller may actuate the BTCC valve to open (or increase a frequencyof modulating the opening/closing of the BTCC valve) and/or thecontroller may advance the exhaust cam timing. In another example, thecontroller may adjust a position of the BTCC valve, exhaust cam timing,and/or intake cam timing in response to the determined total flow offresh air in order to achieve a desired blowthrough air (e.g., freshair) flow to the intake via the scavenge EGR passage. For example, ifthe determined total flow of fresh air is less than the desiredblowthrough air, the controller may actuate the BTCC valve to open,retard exhaust cam timing, and/or advance intake cam timing. In yetanother example, the controller may adjust fuel injection timing and/orfuel injection amounts based on the determined total flow of fuel to theintake via the scavenge EGR passage. The desired flow amounts discussedabove and further below (e.g., with regard to FIG. 8) may be determinedbased on engine operating conditions such as engine speed and loadand/or mass air flow.

Turning to FIG. 8, a graph 800 shows adjustments to engine operatingparameters based on changes in the determined total flows of burnt gas,fresh air, and unburned hydrocarbons through the scavenge EGR passage.Specifically, graph 800 shows changes in valve opening overlap betweenthe scavenge valves and intake valves (e.g., amount of valve openingoverlap between the scavenge valves and intake valves, referred to belowas SV-IV overlap) at plot 802, changes in pressure drop from the intakemanifold to scavenge manifold (e.g., pressure drop across the “variableorifice” created by the overlap period between the intake valves andscavenge valves) at plot 804, changes in total flow (total bulk flow)through the scavenge EGR passage (e.g., total SC-EGR flow) at plot 806,changes in the SC-EGR constituent flows, including burnt gas flow atplot 808, unburned hydrocarbons flow at plot 810, and fresh air flow atplot 812, changes in a position of the BTCC valve (e.g., valve 54arranged in the scavenge EGR passage shown in FIG. 1) at plot 814, andchanges in scavenge valve timing (e.g., exhaust cam timing) at plot 816.

Before time t1, the SV-IV overlap is relatively low (plot 802) and as aresult, the total SC-EGR flow is relatively low (plot 806), with ahigher amount of burnt gas flow (plot 808) and lower amount of fresh airflow (plot 812). Just before time t1, the desired flow of burnt gasesrecirculated to the intake passage may decrease relative to the actualburnt gas flow (plot 808). In response to this condition, the controllermay actuate a cam timing actuator to retard the scavenge valve timing attime t1 (plot 816). In response to retarding the scavenge valve timingat time t1, the SV-IV overlap increases, thereby increasing the totalSC-EGR flow (plot 806), reducing the burnt gas flow (plot 808), andincreasing the fresh air flow (plot 812).

At time t2, the pressure drop between the intake manifold and scavengemanifold decreases (plot 804), causing the total SC-EGR flow to decrease(plot 806). Before time t3, the desired flow of fresh air recirculatedto the intake passage (e.g., blowthrough air) may increase relative tothe actual fresh air flow (plot 812). Thus, in response, at time t3, thecontroller may actuate the cam timing actuator to further retard thescavenge valve timing (plot 816).

Just before time t4, the desired burnt gas flow to the intake passagemay increase relative to the actual burnt gas flow (plot 808). Inresponse to this condition, the controller may actuate the cam timingactuator to advance the scavenge valve timing (plot 816), therebyresulting in a decrease in the SV-IV overlap (plot 802), which resultsin a decrease in the total SC-EGR flow (plot 806), an increase in theburnt gas flow (plot 808), and a decrease in the fresh air flow (plot812).

While adjustments in scavenge valve timing (e.g., exhaust cam timing)responsive to changes in the determined SC-EGR constituent flows areshown in FIG. 8, in alternate embodiments, the controller mayadditionally or alternatively adjust intake valve timing and/or aposition of the BTCC valve responsive to the changes in SC-EGRconstituent flows.

In this way, the total flow through a scavenge EGR passage, routedbetween a scavenge exhaust manifold and the intake passage, upstream ofa compressor, may be determined based on valve opening overlap areabetween the scavenge valves and intake valves and a pressure differencebetween the intake manifold and scavenge manifold. This determinationmay be performed via pressure measurements in the intake manifold andscavenge manifold, but without use of a delta pressure measurementsystem (as described above). As a result, the total flow may bedetermined in a more efficient manner, with existing engine sensors andwithout limiting engine performance and high load conditions. Further,by utilizing engine mapping to determine a relationship between scavengemanifold mass fractions of the scavenge manifold gas portions (e.g.,pushback gases, combustion products, and intake manifold gases) andvalve overlap between the scavenge valves and intake valves, and thedetermined total flow through the scavenge EGR passage, finalconcentrations and flow values of each of burnt gases, unburnedhydrocarbons, and fresh air recirculated through the scavenge EGRpassage may be determined. These flow values may then be used to controlthe engine to deliver desired amounts of burnt gases and freshblowthrough air to the intake passage. For example, engine operatingparameter adjustments may be made in response to the determined totalflows of each of the burnt gases, unburned hydrocarbons, and fresh airin order to increase engine efficiency. The technical effect ofadjusting engine operation in response to a flow of gases to an intakepassage, upstream of a compressor, from a scavenge manifold coupled toscavenge exhaust valves, the flow of gases determined based on a valveopening overlap between the scavenge exhaust valves and intake valves ofan engine, the scavenge exhaust valves opened at a different time thanblowdown exhaust valves coupled to a blowdown manifold coupled to aturbine is increasing engine efficiency while not limiting engineperformance at high load conditions.

As one embodiment, a method includes adjusting engine operation inresponse to a flow of gases to an intake passage, upstream of acompressor, from a scavenge manifold coupled to scavenge exhaust valves,the flow of gases determined based on a valve opening overlap betweenthe scavenge exhaust valves and intake valves of an engine, the scavengeexhaust valves opened at a different time than blowdown exhaust valvescoupled to a blowdown manifold coupled to a turbine. In a first exampleof the method, the flow of gases is a total flow of gases from thescavenge manifold to the intake passage, upstream of the compressor, andwherein the total flow of gases is determined based on a valve openingoverlap area between the scavenge exhaust valves and intake valves, thevalve opening overlap area based on a valve lift of the intake valvesand a valve lift of the scavenge exhaust valves at a current crankangle. A second example of the method optionally includes the firstexample and further includes, wherein the total flow of gases if furtherdetermined based on a pressure of an intake manifold and a pressure ofthe scavenge manifold, where the pressures in the intake manifold andscavenge manifold are measured and crank angle aligned to correspond tothe current crank angle for determining the valve opening overlap area.A third example of the method optionally includes one or more of thefirst and second examples and further includes, wherein the determinedflow of gases increases as the valve opening overlap area increases andincreases as a difference between the pressure in the intake manifoldand the pressure in the scavenge manifold increases, and furthercomprising adjusting an engine actuator to increase the flow of gasesfrom the scavenge manifold to the intake passage, upstream of thecompressor, in response to the determined flow of gases being less thana desired flow of gases. A fourth example of the method optionallyincludes one or more of the first through third examples and furtherincludes, wherein the flow of gases to the intake passage from thescavenge manifold includes individual flows of each of burnt gases,unburned hydrocarbons, and fresh air, and wherein the valve openingoverlap is an amount of valve opening overlap between the scavengeexhaust valves and the intake valves. A fifth example of the methodoptionally includes one or more of the first through fourth examples andfurther includes, wherein adjusting engine operation includes adjustingone or more of a position of a valve disposed in a passage coupledbetween the scavenge manifold and the intake passage, upstream of thecompressor, a timing of the scavenge exhaust valves, and a timing of theintake valves. A sixth example of the method optionally includes one ormore of the first through fifth examples and further includes, whereinadjusting engine operation includes adjusting an engine actuator inresponse to the determined flow of gases and based on a desired flow ofcombusted gases and a desired flow of fresh blowthrough air to theintake passage, upstream of the compressor, from the scavenge manifold.A seventh example of the method optionally includes one or more of thefirst through sixth examples and further includes determining aconcentration of each of burnt gases, unburned hydrocarbons, and freshair in the determined flow of gases based on an amount of valve openingoverlap between the scavenge valves and intake valves and furthercomprising adjusting an engine operating parameter based on thedetermined flow of gases and the determined concentration of each ofburnt gases, unburned hydrocarbons, and fresh air. An eighth example ofthe method optionally includes one or more of the first through seventhexamples and further includes, wherein adjusting the engine operatingparameter includes adjusting one or more of a fuel injection timing oramount, a position of a valve arranged in a passage between the scavengemanifold and the intake passage, upstream of the compressor, a positionof a valve arranged in a bypass passage coupled between the scavengemanifold and an exhaust passage, downstream of the turbine, an exhaustcam timing, and an intake cam timing.

As another embodiment, a method includes adjusting an engine operatingparameter based on a total flow of gases to an intake passage, upstreamof a compressor, from a scavenge manifold coupled to scavenge exhaustvalves, the total flow of gases determined based on a valve openingoverlap area between the scavenge exhaust valves and intake valves of anengine and pressures in each of an intake manifold and the scavengemanifold, the scavenge exhaust valves opened at a different time thanblowdown exhaust valves coupled to a blowdown manifold coupled to aturbine. In a first example of the method, the valve opening overlaparea is determined based on a valve lift of the scavenge exhaust valvesand a valve lift of the intake valves at a current crank angle. A secondexample of the method optionally includes the first example and furtherincludes, wherein the pressures in each of the intake manifold and thescavenge manifold are measured at the current crank angle. A thirdexample of the method optionally includes one or more of the first andsecond examples and further includes, adjusting the measured pressure ofthe scavenge manifold based on engine speed. A fourth example of themethod optionally includes one or more of the first through thirdexamples and further includes, determining a concentration of burnt gas,a concentration of unburned hydrocarbons, and a concentration of freshair within the total flow of gases based on an amount of valve openingoverlap between the scavenge exhaust valves and intake valves, andwherein adjusting the engine operating parameter includes adjusting theengine operating parameter based on individual flows of each of theburnt gas, unburned hydrocarbons, and fresh air, which are based on thedetermine concentrations of burnt gas, unburned hydrocarbons, and freshair, respectively, and the determined total flow of gases. A fifthexample of the method optionally includes one or more of the firstthrough fourth examples and further includes, wherein adjusting theengine operating parameter includes adjusting a timing of one or more ofthe scavenge exhaust valves and the intake valves. A sixth example ofthe method optionally includes one or more of the first through fifthexamples and further includes, wherein adjusting the engine operatingparameter includes adjusting a position of a valve disposed in a passagecoupled between the scavenge manifold and the intake passage, upstreamof the compressor. A seventh example of the method optionally includesone or more of the first through sixth examples and further includes,wherein adjusting the engine operating parameter includes adjusting aposition of a valve disposed in a bypass passage coupled between thescavenge manifold and an exhaust passage, downstream of the turbine, theexhaust passage coupled to the blowdown manifold.

As yet another embodiment, a system for an engine includes a pluralityof cylinders, each including an intake valve, a scavenge exhaust valve,and a blowdown exhaust valve; an intake manifold coupled to the intakevalve of each cylinder; a scavenge manifold coupled to the scavengeexhaust valve of each cylinder and an intake passage, upstream of acompressor, via a scavenge exhaust gas recirculation passage; a blowdownmanifold coupled to the blowdown exhaust valve of each cylinder and anexhaust passage including a turbine; and a controller with computerreadable instructions stored on non-transitory memory that when executedduring engine operation, cause the controller to: determine a total flowof gases through the scavenge exhaust gas recirculation passage, fromthe scavenge manifold to the intake manifold, upstream of thecompressor, based on a valve opening overlap area between the scavengeexhaust valve and intake valve; and adjust an operating parameter of theengine based on the determined total flow of gases. In a first exampleof the system, the total flow of gases is further determined based on ameasured pressure in the intake manifold and a measured pressure in thescavenge manifold. A second example of the system optionally includesthe first example and further includes, wherein the valve openingoverlap area is determined based on a valve lift of the scavenge valveand a valve lift of the intake valve at a current crank angle, andwherein the operating parameter that is adjusted includes one or more ofa timing of the scavenge valve, a timing of the intake valve, and aposition of a valve disposed in the scavenge exhaust gas recirculationpassage.

Note that the example control and estimation routines included hereincan be used with various engine and/or vehicle system configurations.The control methods and routines disclosed herein may be stored asexecutable instructions in non-transitory memory and may be carried outby the control system including the controller in combination with thevarious sensors, actuators, and other engine hardware. The specificroutines described herein may represent one or more of any number ofprocessing strategies such as event-driven, interrupt-driven,multi-tasking, multi-threading, and the like. As such, various actions,operations, and/or functions illustrated may be performed in thesequence illustrated, in parallel, or in some cases omitted. Likewise,the order of processing is not necessarily required to achieve thefeatures and advantages of the example embodiments described herein, butis provided for ease of illustration and description. One or more of theillustrated actions, operations and/or functions may be repeatedlyperformed depending on the particular strategy being used. Further, thedescribed actions, operations and/or functions may graphically representcode to be programmed into non-transitory memory of the computerreadable storage medium in the engine control system, where thedescribed actions are carried out by executing the instructions in asystem including the various engine hardware components in combinationwith the electronic controller.

It will be appreciated that the configurations and routines disclosedherein are exemplary in nature, and that these specific embodiments arenot to be considered in a limiting sense, because numerous variationsare possible. For example, the above technology can be applied to V-6,I-4, I-6, V-12, opposed 4, and other engine types. The subject matter ofthe present disclosure includes all novel and non-obvious combinationsand sub-combinations of the various systems and configurations, andother features, functions, and/or properties disclosed herein.

As used herein, the term “approximately” is construed to mean plus orminus five percent of the range unless otherwise specified.

The following claims particularly point out certain combinations andsub-combinations regarded as novel and non-obvious. These claims mayrefer to “an” element or “a first” element or the equivalent thereof.Such claims should be understood to include incorporation of one or moresuch elements, neither requiring nor excluding two or more suchelements. Other combinations and sub-combinations of the disclosedfeatures, functions, elements, and/or properties may be claimed throughamendment of the present claims or through presentation of new claims inthis or a related application. Such claims, whether broader, narrower,equal, or different in scope to the original claims, also are regardedas included within the subject matter of the present disclosure.

1. A method, comprising: adjusting engine operation in response to aflow of gases to an intake passage, upstream of a compressor, from ascavenge manifold coupled to scavenge exhaust valves, the flow of gasesdetermined with instructions executed by a processor based on a valveopening overlap between the scavenge exhaust valves and intake valves ofan engine, the scavenge exhaust valves opened at a different time thanblowdown exhaust valves coupled to a blowdown manifold coupled to aturbine.
 2. The method of claim 1, wherein the flow of gases is a totalflow of gases from the scavenge manifold to the intake passage, upstreamof the compressor, and wherein the total flow of gases is determinedwith the instructions executed by the processor based on a valve openingoverlap area between the scavenge exhaust valves and the intake valves,the valve opening overlap area based on a valve lift of the intakevalves and a valve lift of the scavenge exhaust valves at a currentcrank angle.
 3. The method of claim 2, wherein the total flow of gasesis further determined with the instructions executed by the processorbased on a pressure of an intake manifold and a pressure of the scavengemanifold, where the pressures in the intake manifold and the scavengemanifold are measured and crank angle aligned to correspond to thecurrent crank angle for determining the valve opening overlap area. 4.The method of claim 3, wherein the determined flow of gases increases asthe valve opening overlap area increases and increases as a differencebetween the pressure in the intake manifold and the pressure in thescavenge manifold increases, and further comprising adjusting an engineactuator to increase the flow of gases from the scavenge manifold to theintake passage, upstream of the compressor, in response to thedetermined flow of gases being less than a desired flow of gases.
 5. Themethod of claim 1, wherein the flow of gases to the intake passage fromthe scavenge manifold includes individual flows of each of burnt gases,unburned hydrocarbons, and fresh air, and wherein the valve openingoverlap is an amount of valve opening overlap between the scavengeexhaust valves and the intake valves.
 6. The method of claim 1, whereinadjusting the engine operation includes adjusting one or more of aposition of a valve disposed in a passage coupled between the scavengemanifold and the intake passage, upstream of the compressor, a timing ofthe scavenge exhaust valves, and a timing of the intake valves.
 7. Themethod of claim 1, wherein adjusting the engine operation includesadjusting an engine actuator in response to the determined flow of gasesand based on a desired flow of combusted gases and a desired flow offresh blowthrough air to the intake passage, upstream of the compressor,from the scavenge manifold.
 8. The method of claim 1, further comprisingdetermining, with the instructions executed by the processor, aconcentration of each of burnt gases, unburned hydrocarbons, and freshair in the determined flow of gases based on an amount of valve openingoverlap between the scavenge valves and the intake valves and furthercomprising adjusting an engine operating parameter based on thedetermined flow of gases and the determined concentration of each ofburnt gases, unburned hydrocarbons, and fresh air.
 9. The method ofclaim 8, wherein adjusting the engine operating parameter includesadjusting one or more of a fuel injection timing or amount, a positionof a valve arranged in a passage between the scavenge manifold and theintake passage, upstream of the compressor, a position of a valvearranged in a bypass passage coupled between the scavenge manifold andan exhaust passage, downstream of the turbine, an exhaust cam timing,and an intake cam timing.
 10. A method, comprising: adjusting an engineoperating parameter based on a total flow of gases to an intake passage,upstream of a compressor, from a scavenge manifold coupled to scavengeexhaust valves, the total flow of gases determined with instructionsexecuted by a processor based on a valve opening overlap area betweenthe scavenge exhaust valves and intake valves of an engine and pressuresin each of an intake manifold and the scavenge manifold, the scavengeexhaust valves opened at a different time than blowdown exhaust valvescoupled to a blowdown manifold coupled to a turbine.
 11. The method ofclaim 10, wherein the valve opening overlap area is determined with theinstructions executed by the processor based on a valve lift of thescavenge exhaust valves and a valve lift of the intake valves at acurrent crank angle.
 12. The method of claim 11, wherein the pressuresin each of the intake manifold and the scavenge manifold are measured atthe current crank angle.
 13. The method of claim 12, further comprisingadjusting the measured pressure of the scavenge manifold based on enginespeed.
 14. The method of claim 10, further comprising determining, withthe instructions executed by the processor, a concentration of burntgas, a concentration of unburned hydrocarbons, and a concentration offresh air within the total flow of gases based on an amount of valveopening overlap between the scavenge exhaust valves and the intakevalves, and wherein adjusting the engine operating parameter includesadjusting the engine operating parameter based on individual flows ofeach of the burnt gas, unburned hydrocarbons, and fresh air, which arebased on the determined concentrations of burnt gas, unburnedhydrocarbons, and fresh air, respectively, and the determined total flowof gases.
 15. The method of claim 10, wherein adjusting the engineoperating parameter includes adjusting a timing of one or more of thescavenge exhaust valves and the intake valves.
 16. The method of claim10, wherein adjusting the engine operating parameter includes adjustinga position of a valve disposed in a passage coupled between the scavengemanifold and the intake passage, upstream of the compressor.
 17. Themethod of claim 10, wherein adjusting the engine operating parameterincludes adjusting a position of a valve disposed in a bypass passagecoupled between the scavenge manifold and an exhaust passage, downstreamof the turbine, the exhaust passage coupled to the blowdown manifold.18. A system for an engine, comprising: a plurality of cylinders, eachincluding an intake valve, a scavenge exhaust valve, and a blowdownexhaust valve; an intake manifold coupled to the intake valve of eachcylinder; a scavenge manifold coupled to the scavenge exhaust valve ofeach cylinder and an intake passage, upstream of a compressor, via ascavenge exhaust gas recirculation passage; a blowdown manifold coupledto the blowdown exhaust valve of each cylinder and an exhaust passageincluding a turbine; and a controller with computer readableinstructions stored on non-transitory memory that when executed duringengine operation, cause the controller to: determine a total flow ofgases through the scavenge exhaust gas recirculation passage, from thescavenge manifold to the intake manifold, upstream of the compressor,based on a valve opening overlap area between the scavenge exhaust valveand the intake valve; and adjust an operating parameter of the enginebased on the determined total flow of gases.
 19. The system of claim 18,wherein the total flow of gases is further determined based on ameasured pressure in the intake manifold and a measured pressure in thescavenge manifold.
 20. The system of claim 18, wherein the valve openingoverlap area is determined based on a valve lift of the scavenge valveand a valve lift of the intake valve at a current crank angle, andwherein the operating parameter that is adjusted includes one or more ofa timing of the scavenge valve, a timing of the intake valve, and aposition of a valve disposed in the scavenge exhaust gas recirculationpassage.